Leak detector comprising an inlet

ABSTRACT

A leak detector includes an inlet, a high-vacuum pump, and a test gas detector, which is connected to the entry of the high-vacuum pump. A backing pump is connected to an outlet area of the high-vacuum pump, and a test gas line extends between the inlet of the leak detector and the backing pump, the test gas line being connected to the outlet area of the high-vacuum pump via a line section. In order to shorten the response time of the leak detector, the line and the backing pump are connected via separate connections to the outlet area of the high-vacuum pump.

FIELD OF THE INVENTION

The present invention relates to a leak detector.

BACKGROUND OF THE INVENTION

Leak detectors are known from publications DE-C2 31 24 205, DE-A1 42 28313 and DE-A1 195 23 430. These are counterflow leak detectors which arecommonly operated with helium as the test gas. During leak detectionoperation, the gas which in the instance of a defective device undertest contains the test gas, flows through a line from the inlet of theleak detector to the backing pump. This line is connected through linesections to at least the outlet area of the high-vacuum pump, preferablyalso with a pressure stage. Depending on which of the line sections isopen, leak detection is performed at a different sensitivities.

Generally there exists the problem where in the instance of leakdetectors of this kind the response time, i.e. the time which elapsesfrom the point of time when the test gas enters into the inlet of theleak detector until the point of time when the test gas is recorded, isrelatively long and specifically so at higher pressures. From EP-B1 752095 a leak detector is known where its inlet is connected via a test gasline to a gas supply pump. For the connection of the test gas line tothe outlet area of the high-vacuum pump, a connection port equipped witha coaxial line is provided. Such a solution is design-wise involved andoffers only a limited conductivity.

SUMMARY OF THE INVENTION

It is the task of the present invention to attain the desired reductionin the response time in the instance of counterflow leak detectionwithin the upper pressure range by a more simple solution.

This task is solved in accordance with the present invention.

In that in the instance of a defective device under test, the entiretest gas containing gas flows through the outlet area of the high-vacuumpump (respectively through a pressure stage) the path across which thetest gas needs to diffuse is reduced thereby reducing the response timeto a minimum.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the present invention shall beexplained with reference to the examples of embodiments depicitedschematically in the drawing in which:

FIG. 1 depicts a leak detector with a high-vacuum pump designed by wayof a compound pump, the molecular pumping stage which is of a singlestage design; and

FIGS. 2 and 3 depict a leak detector in accordance with the presentinvention with a compound pump, the molecular pumping stage of which inturn is of a multiple stage design.

DETAILED DESCRIPTION

Components of the depicted leak detectors 1 with their inlet 2, are thehigh-vacuum pump 3 designed by way of a compound drag pump. Compounddrag pump means that it is equipped with a turbomolecular pumping stageand a molecular pumping stage. Preferably pumps of this kind are of asingle flow design, i.e. their stages are arranged axially the one afterthe other in the direction of the pumping action.

The outer housing of the high-vacuum pump 3 is designated as 11. Saidhousing is equipped with a central bearing bushing 12 projecting towardsthe inside in which a shaft 13 is supported by means of a spindlebearing 14, for example. Linked to the shaft 13 are the drive motor 15,the rotor 16 of a molecular pumping stage as well as the rotor 17 of aturbomolecular pumping stage. Basis of the pump is a chassis 20, whichsupports the housing 11, the bearing bushing 12 and the stator of thedrive motor 15.

The rotor 17 is equipped with the rotor blades 18, which jointly withthe stator blades 19 mounted in the housing 11 form the turbomolecularpumping stage. By means of the flange 4, the pump is connected to thetest gas detector 6 depicted only schematically, which commonly is amass spectrometer.

In the example of the embodiment in accordance with drawing FIG. 1, themolecular pump (respectively pumping stage) comprises the bell-shapedrotor 16 spanning the motor/bearing chamber 7, said rotor 16 beingequipped on its outside with thread-like grooves 8 in which duringoperation of the pump the gas is conveyed from the high-vacuum side tothe forevacuum side. Assigned to the rotor 16 is a stator 9 ofapproximately the same axial length. Located between the stator 9 andthe rotor 16 is the gap 10. This needs to be as small as possible so asto attain a good seal between the thread grooves. Connected to theforevacuum chamber 21 is the forevacuum port 22. The backing pump isdesignated as 43.

To the stator 31 of the turbomolecular pumping stage 18/19 there areassigned the rotor blades 19 and the spacing rings 32 to 34. The statorblades 19 are, in a basically known manner, components of blade rings orblade ring sections 35 with outer rims 36, which in the mounted state ofthe stator are located between the spacing rings. The stator made ofalternatingly arranged spacing rings 32 and blade rings 35 above eachother, is centred through the outer housing 11.

In drawing FIG. 1, a compound pump is depicted as an example which pumpsthe taken in gases (inlet flange 4) along the longitudinal axis of thepump in a single flow in the direction of chassis 20. Within the scopeof the present invention the high-vacuum pump may also be designedcompletely as a turbomolecular pump or a molecular pump.

The turbomolecular pumping stage 18, 19 is equipped with an intermediateinlet 38 serving the purpose of admitting the test gas when employingthe pump in a counterflow leak detector. The spacing rings 33, 34located at the level of the intermediate inlet 38 have been modifiedcompared to the remaining spacing rings 32. One or both spacing rings33, respectively 34 exhibit a reduced outside diameter and form jointlywith the housing 11 the circumferential annular channel 41 into whichthe intermediate inlet 38 opens out. The spacing ring(s) 33,respectively 34 with reduced outside diameter, exhibit moreover passages42 through which the connection of the pumping chamber of theturbomolecular pumping stage with the intermediate inlet 38 isestablished. These passages may, for example, be several bores asdepicted in the instance of spacing ring 34. An other possibility existsin that a spacing ring 33 is milled such that it section-wise exhibits areduced (axial) height. The manufacture of passages with a highconductance is thus possible.

A further test gas inlet 45 is located at the level of the molecularpumping stage 9/16, and specifically approximately at half the height ofthis pumping stage. Finally a further test gas inlet 46 is arranged atthe level of the outlet area of the high-vacuum pump 3. Said test gasinlet opens out into the substantially ring-shaped forevacuum chamber 21which follows the pump cross-section, gap 10.

As in the instance of leak detectors in accordance with thestate-of-the-art there follows at the inlet 2 of the leak detector 1 thetest gas line 47 which is linked through the line sections 48, 49, 51each equipped with a valve 52, 53 respectively 54 to the test gas inlets38, 45, 46. Moreover, the test gas line 47 is linked through linesection 55 with the valve 56 with the backing pump 43.

Located at the level of the connection ports 45 and 46 are the furtherconnection ports 57 and 22. These are connected through the linesections 58, 59 each equipped with a valve 61, respectively 62, to theforevacuum line 63 into which also the line section 55 opens out.

At the inlet 2, a device under test which is sprayed from the outsidewith test gas, or a chamber with one or several devices under test canbe connected which each contain test gas. Leak detection is performed insuch a manner that initially the device under test, respectively thetest chamber is pre-evacuated with valve 56 being open—all other valvesare closed. Gross leak detection can commence at a very early stage andspecifically by opening the valves 54 and 62.

Almost the entire quantity of gas flowing in the test gas line, in theinstance of a closed valve 56 the entire quantity of gas, flows throughthe forevacuum chamber 21 expediently designed by way of an annularchannel. The test gas contained in the flowing gas thereby passes morerapidly and at higher concentration compared to the state-of-the-artinto the forevacuum chamber of the high-vacuum pump and thus also morerapidly towards the test gas detector 6.

An even higher level of sensitivity is attained when the valve54—expediently also the valve 62—is closed and where the valves 53, 61are opened. Also the valve 56 is—as already detailed—closed. In thisoperating mode the entire quantity of gas flowing through the test gasline 47 flows approximately at half the height through the molecularpumping stage 9, 16. Located expediently at the level of the connectionports 45, 57 is an annular channel 64 so as to reduce the flowresistance.

Finally the highest sensitivity level of the leak detection process isattained in a basically known manner by opening the valve 52. Thepressure of the high-vacuum pump at this point is low (for example ≦10⁻¹mbar) and thus the diffusion velocity of the test gas is high. Andappreciable improvement in the response time would not be attained ifthe entire gas flowing in the test gas line 47 were to flow through theturbomolecular pumping stage.

Expediently the connection ports 46, 22 (respectively 45, 57) opposeeach other so that possibly present test gas can reach, as rapidly aspossible, the entire outlet cross section (gap 10 in the depictedexample of an embodiment or, if only blade stages are present, theblades on the outlet side). However, very good results are still alsoattained when the axes of the connections form an angle of 90° (andless).

A significant reduction in the response time is already attained in thatfor the purpose of connecting the backing pump 43 and the feed in of thegas possibly containing the test gas into the forevacuum area of thehigh-vacuum pump 1, two separate connection ports 22, 46 are present.This advantage continues to exist also when the connection ports 45 and57 as well as the related connection lines 49, 58 with their valves 52,61 are not present.

Drawing FIG. 2 depicts highly schematically a leak detection facility inaccordance with the present invention with a compound pump. It isequipped with a turbomolecular pumping stage 18, 19 and the molecularpumping stage 9, 16 followed by a further molecular pumping stage. Tothis end the bell-shaped rotor is equipped with a smooth cylindersection. Assigned to its wall is from the outside the stator section 9,equipped with a thread which together with the outer wall of the rotor 9forms the pumping gap 10. A further stator section 70 with its thread 71is assigned to the inside of the rotor cylinder. This molecular pumpingsection 16, 70 is so designed that the direction of the gases pumped inpumping gap 72 is opposed to the direction of the pumping action in gap10. From this it results that the discharge area 21 of the high-vacuumpump has a distance from the chassis 20. Said discharge area is locatedabove the bearing bushing 12 and is substantially cylindrical in shape.Via annular chamber 73 and encompassing the bearing bushing 12 it islinked to the connection ports 46, 22 these being arranged at chassis20. The outlet area 21 and the annular chamber 73 are components of thebearing/motor chamber 7.

In the example of the embodiment in accordance with drawing FIG. 2, theinlet 2 of the leak detector 1 is linked through line 47, 55 with theconnection port 46. During the leak detection process, gas possiblycontaining the test gas flows through the connection port 46 via theannular chamber 73 to the outlet area 21 and from there again throughthe annular chamber 73 and the connection port 22 to the backing pump43. So that areas close to the chassis of the annular chamber 73 willnot cause any flow short-circuits between the ports 46 and 22, it isexpedient that the annular chamber 73 be equipped with separating meansnot depicted, for example axially extending separating walls, whichensure that the entire quantity of gas entering into connection port 46is pumped through the outlet area 21 of the high-vacuum pump.

Drawing FIG. 3 depicts an example of an embodiment in which, like in theexample of the embodiment in accordance with drawing FIG. 2, themolecular pump is of a two-stage design. Besides the connections 46 and22 there are—as in the example of the embodiment in accordance withdrawing FIG. 1—present the further connections 38, 45 and 57. Theconnections 45 and 57 open out into the pumping chamber of the two-stagemolecular pumping stage, and specifically in the transition area ofthese stages 16, 9 and 16, 70, i.e. there, where the flowing gaseschange their direction by approximately 180°.

1. A leak detector comprising: an inlet; a high-vacuum pump; a test gasdetector connected to an inlet of the high-vacuum pump; a backing pumpconnected to an outlet area of the high-vacuum pump; and a test gas linerunning between the inlet of the leak detector and the backing pump,said test gas line being connected to the outlet area of the high-vacuumpump via a line section and in which the line section and the backingpump are connected via separate connection ports to the outlet area ofthe high-vacuum pump.
 2. A leak detector in accordance with claim 1,wherein an outlet chamber located within a housing of the high-vacuumpump forms the outlet area of the high-vacuum pump and where the housingof the high-vacuum pump is equipped with said two separate connectionports that are connected to the outlet chamber.
 3. A leak detector inaccordance with claim 1, wherein the outlet chamber is located in thevicinity of a chassis of the high-vacuum pump.
 4. A leak detector inaccordance with claim 3, wherein the high-vacuum pump is a single flowdesign and where an inlet flange and the chassis of the high-vacuum pumpoppose one another.
 5. A leak detector in accordance with claim 2,wherein the outlet chamber has the shape of an annular channel.
 6. Aleak detector in accordance with claim 1, wherein the high-vacuum pumpis a turbomolecular vacuum pump.
 7. A leak detector in accordance withclaim 6, wherein the turbomolecular vacuum pump is equipped with atleast one additional gas inlet.
 8. A leak detector in accordance withclaim 6, wherein the turbomolecular vacuum pump is equipped with atleast two additional gas inlets.
 9. A leak detector in accordance withclaim 8, wherein there is provided at the same level as one of saidadditional gas inlets, a further connection port that is linked to thebacking pump.
 10. A leak detector in accordance with claim 1, whereinthe high-vacuum pump is a compound vacuum pump having a turbomolecularstage and a molecular pumping stage.
 11. A leak detector in accordancewith claim 10, wherein at the level of the turbomolecular pumping stage,an additional test gas inlet is provided.
 12. A leak detector inaccordance with claim 10, wherein at the level of the molecular pumpingstage, preferably at half the height of this stage, a test gasconnection port is provided.
 13. A leak detector in accordance withclaim 12, wherein at the same level as the test gas connection port, anadditional connection port is provided which is linked to the backingpump.
 14. A leak detector in accordance with claim 13, wherein anannular channel is located at the level of the additional test gasconnection ports.
 15. A leak detector in accordance with claim 10,wherein the molecular pumping stage is of a multi-stage design.
 16. Aleak detector in accordance with claim 15, wherein there is connected toa first molecular pumping stage with a pumping action axially in thedirection of the chassis, a second molecular pumping stage which has anopposing direction of the pumping action such that the outlet area ofthe high-vacuum pump has a distance from the chassis and is connectedthrough an annular chamber to the connection port to which the backingpump is connected and where also the connection port connected via thevalve with the test gas line is connected to the annular chamber.
 17. Aleak detector in accordance with claim 16, wherein the outlet area ofthe high-vacuum pump is defined by a substantially cylindrical chamberinto which the second molecular pumping stage opens out and which isconnected to the annular chamber.
 18. A leak detector in accordance withclaim 13, wherein each of said connection ports located at the sameheight are arranged with respect to the longitudinal axis of thehigh-vacuum pump on the side and form an angle ranging between 35° and180°.
 19. A leak detector in accordance with claim 18, wherein theconnection ports oppose each other.